Alterations in Monoclonal Antibody Affinity and Antigenic Receptor Site Expression on Mycoplasma-Infected Human Colorectal Cancer Cells

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The affinity of MoAb CO 17–1A and expression of its antigenic target were studied on uninfected and mycoplasma-infected colorectal cancer cell lines SW 1116 and SW 948. Binding of 125I-labeled CO 17–1A to SW 1116 cells was quantified at 37°C by determination of the affinity constant (Ka) and the number of antigenic receptor sites (r) per cell using Scatchard plots. When mycoplasma-free SW 1116 cells were used as targets, Ka was 0.92 ± 0.06 × 108M -1 and r = 1.32 ± 0.14 × 106 at 37°C. One batch of unspeciated, mycoplasma-infected SW 1116 cells had reduced affinity and a decreased number of antigenic receptor sites per cell for 125I-labeled 17–1A, while another batch of infected SW 1116 cells had a 4- to 5-fold increase in r and diminished Ka for the antibody compared with uninfected cells. When unspeciated, mycoplasma-infected SW 948 cells were exposed to 125I-labeled 17–1A and the data subjected to Scatchard analysis, the affinity of the antibody deviated markedly from linearity and rendered analysis for Ka and r meaningless. These data indicate that mycoplasma infection can produce variable effects on the cellular expression of antigenic receptor sites and the affinity of antibody for its target, and emphasize the importance of using mycoplasma-free cell lines in studies of these parameters. © 1990, SAGE Publications. All rights reserved.

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